<p>
Rules for using primitive data types and wrapper classes:
 1) Members of a POJO class must be wrapper classes.
 2) The return value and arguments of a RPC method must be wrapper classes.
 3) [Recommended] Local variables should be primitive data types.
<p>
<p>Examples:</p>
<pre>
    public class DemoDO {
        String str;
        Integer a;
    }
</pre>